The Experts below are selected from a list of 225 Experts worldwide ranked by ideXlab platform

Máximo Barón - One of the best experts on this subject based on the ideXlab platform.

V. Val. Sobolev - One of the best experts on this subject based on the ideXlab platform.

  • Dielectric Spectra and d-bands Structure of Germanium, Tin, and Lead Tellurides
    Russian Physics Journal, 2021
    Co-Authors: D. A. Perevoshchikov, V. Val. Sobolev, A. I. Kalugin, E. A. Antonov
    Abstract:

    The known experimental absorption spectra were used to calculate the dielectric spectra of GeTe, SnTe, and PbTe crystals in the region of electron transitions from the core d-bands of cations. Their characteristic features and general regularities are revealed. Using the combined Argand Diagram method, the dielectric spectra of each crystal were decomposed into six elementary oscillators and their main parameters were determined. The nature of formation of these oscillators is proposed on the basis of the theory of interband and exciton transitions.

  • Fundamental Optical Functions and Fine-Structure Parameters of Strontium–Selenide Crystal Transition Bands in the 0–40 eV Range
    Journal of Applied Spectroscopy, 2018
    Co-Authors: V. V. Sobolev, D. A. Merzlyakov, V. Val. Sobolev
    Abstract:

    The spectral complex of fundamental optical functions of strontium-selenide (SrSe) crystal in the range 0–40 eV was determined. Spectra of the imaginary parts of three functions [transverse dielectric permittivity e2(E) and longitudinal volume –Im e–1 and surface –Im (1 + e)–1 characteristic electron energy losses] of SrSe crystal were deconvoluted into 36 elementary bands. Energies of maxima Ei, half-widths Hi, amplitudes Ii, areas Si, and oscillator strengths fi were determined for every band of the three spectra. The main spectral features of the optical functions and 36 elementary bands of SrSe in the range 3–35 eV due to excitons and transverse and longitudinal interband transitions were established. The calculations were based on experimental reflectance spectra and used the Kramers–Kronig integral relations, a modified combined Argand Diagram method, and a number of computer programs.

  • Fundamental Optical Functions and Fine-Structure Parameters of Strontium–Selenide Crystal Transition Bands in the 0–40 eV Range
    Journal of Applied Spectroscopy, 2018
    Co-Authors: V. V. Sobolev, D. A. Merzlyakov, V. Val. Sobolev
    Abstract:

    The spectral complex of fundamental optical functions of strontium-selenide (SrSe) crystal in the range 0–40 eV was determined. Spectra of the imaginary parts of three functions [transverse dielectric permittivity ε_2( E ) and longitudinal volume –Im ε^–1 and surface –Im (1 + ε)^–1 characteristic electron energy losses] of SrSe crystal were deconvoluted into 36 elementary bands. Energies of maxima E _ i , half-widths H _ i , amplitudes I _ i , areas S _ i , and oscillator strengths f _ i were determined for every band of the three spectra. The main spectral features of the optical functions and 36 elementary bands of SrSe in the range 3–35 eV due to excitons and transverse and longitudinal interband transitions were established. The calculations were based on experimental reflectance spectra and used the Kramers–Kronig integral relations, a modified combined Argand Diagram method, and a number of computer programs.

  • Optical Transitions in ZnSe and CdTe Crystals with Involvement of the Cation d Bands
    Semiconductors, 2018
    Co-Authors: V. Val. Sobolev, D. A. Perevoshchikov
    Abstract:

    The permittivity spectra e1(E) and e2(E) of ZnSe and CdTe crystals are calculated in the range of 10–25 eV using their experimental reflectance spectra and Kramers–Kronig integral relations. The spectra are decomposed into thirteen and twelve separate transition bands for ZnSe and CdTe, respectively, using the improved nonparametric combined Argand Diagram technique. The main spectral parameters, including the maximum energies and halfwidths and oscillator strengths, are determined. The oscillator strengths are found to be within 0.1–1.4 for ZnSe and 0.2–0.7 for CdTe. The obtained e2(E) bands are due to interband and exciton transitions with the involvement of cation core d bands of both crystals under consideration.

  • Study of the Optical Properties of Barium Selenide Crystals. II. Elementary Transition Bands and Their Fundamental Parameters
    Journal of Applied Spectroscopy, 2017
    Co-Authors: V. V. Sobolev, D. A. Merzlyakov, V. Val. Sobolev
    Abstract:

    The spectral dependences of the imaginary parts of the dielectric permittivity ε_2(E), bulk (–Im ε^–1) and surface (–Im (1 + ε)^–1) characteristic electron energy losses for a barium selenide crystal are decomposed into 34 elementary bands in the 3–5.5 eV region at 2 K and in the 5.5–26 eV region at 77 K by an improved combined Argand Diagram method. For each band in the three types of spectra, we determined the energy maxima E_i, the half-widths H_i, the amplitudes I_i, the areas S_i, and the oscillator strengths f_i. The parameter f_i is calculated using a modification of the familiar formula for the effective number of valence electrons n_eff (E). We have established the main features of the 34 elementary bands of barium selenide in the 3–26 eV region, due to excitons and transverse and longitudinal interband transitions.

Pascal Rembert - One of the best experts on this subject based on the ideXlab platform.

  • Methods of Isolation of Modal Resonances
    Applied Mechanics Reviews, 1998
    Co-Authors: N. D. Veksler, Jean-marc Conoir, Jean-louis Izbicki, Pascal Rembert
    Abstract:

    The scattering problem by immersed targets involves the resonance phenomenon. Different methods of isolation of modal resonances are discussed: the Resonant Scattering Theory (the different backgrounds used in this method are considered), the phase gradient method (which is partly independent of the background choice), and the Argand Diagram method (leading to both theoretical and experimental determination of the frequency and the width of resonances) and an exact description of the resonance components of partial modes (involving the determination of the roots of the characteristic equation in the complex frequency plane). The results provided by these methods are compared, their validity domain is discussed. Whatever the method, the resonant components appear as Breit-Wigner functions: this is the common point between the different methods. This review article includes 119 references.

  • New experimental characterization of a resonance: Identification of the mode number using the Argand Diagram and the GTD approach
    The Journal of the Acoustical Society of America, 1998
    Co-Authors: Serge Derible, Jean-marc Conoir, Jean-louis Izbicki, Pascal Rembert
    Abstract:

    Until now, the mode n of vibration of an immersed cylindrical shell, associated to the reemission of a peripheral wave, using an incident quasimonochromatic plane wave is performed by carrying out the method of isolation and identification of resonance. The new method proposed here involves only the FFT of the whole pressure signal backscattered at normal incidence by the shell, normalized using the FFT of the incident wideband signal. At a resonance frequency, corresponding to an unknown value of n, the background phase φexp is measured from the Argand Diagram of the scattered pressure. It corresponds to the argument of the pressure at the resonance frequency. The geometrical theory of diffraction allows us to connect the background phase φGTD to the mode number n. This mode is then deduced by minimizing the difference between φexp and φGTD. Experiments are carried out for A and S0 resonances. Then, with a single backscattered signal, it is possible to obtain the frequency, the width, and the mode of the...

  • A new method to determine the transversal wave velocity in thin elastic plates
    Acoustics letters, 1998
    Co-Authors: Guy Durinck, Pascal Rembert, Willy Thys, Jean-louis Izbicki
    Abstract:

    A method to determine the transversal wave velocity in submerged plates is presented. It is based on an analysis of the transmission coefficient of the plate between its first and second critical angles, where the only bulk waves present in the plate are shear waves. According to the resonance theory of plate modes, the parametric representation of the transmission coefficient of a plate in the complex plane (an Argand Diagram) is a circle. It turns out that the experimental Argand Diagram can be given the same orientation as the theoretical Diagram by introducing a time-delay between the transmitted and the reference signal during the normalisation process. Between the first and second critical angles, this time-delay depends on the transversal wave velocity only. We propose to determine the time-delay required for a correct orientation of the Argand Diagram and to calculate from it the transversal wave velocity.

Hicham Banouni - One of the best experts on this subject based on the ideXlab platform.

Hassan Bita - One of the best experts on this subject based on the ideXlab platform.

  • Ultrasound monitoring of a mortar hydration using Argand Diagram: The effect of sand grain size and temperature
    Construction and Building Materials, 2017
    Co-Authors: Hassan Bita, B. Faiz, Ali Moudden, Hicham Lotfi, El Houssaine Ouacha, Hicham Banouni
    Abstract:

    Abstract The reflection technique of ultrasonic waves was used for monitoring and nondestructively characterization of a mortar during its evolution. Using Argand Diagram to measure the resonant ultrasonic wave frequency and its width shows that they follow the rapidly changing in mechanical properties of the material at the young age. Both parameters increase during the time of hardening and also prove the effect of the sand particle size and temperature of the mortar properties. Moreover, measuring the width of the ultrasonic wave resonance allows distinguishing the different hydration phases of material.

  • Evaluation of Ultrasonic Attenuation in Mortars Structures Using the Argand Diagram
    International Journal of Materials Engineering, 2016
    Co-Authors: Hassan Bita, B. Faiz, Ali Moudden, Hicham Lotfi, El Houssaine Ouacha, Mustapha Boutaib
    Abstract:

    The work presents a new method that tracks the total attenuation of the ultrasonic waves in a mortar during hydration. The method is based on a representation in the complex plane of reflection coefficient of waves backscattered by the mortar layer which takes the form of a circle in the vicinity of a resonance. Monitoring the diameter of the circle during all stages of hydration shows its sensitivity to changes in the microstructure of the material. A strong correlation exists between the diameter of the Argand circle and attenuation on samples with different compositions and at different temperatures. The correlation shows the ability of the parameter to detect the physical and chemical changes in the material and its accuracy for differentiating the phases of hydration.